The present invention relates to a projection type projector apparatus using a reflection type liquid crystal panel, such as a so-called liquid crystal projector or projection type television using forward projection.
Liquid crystal projectors for business use have widely spread. Furthermore, as a substitute for a conventional image display apparatus of such a scheme that an image displayed on a cathode-ray tube is projected onto a screen, development of a projection type television using liquid crystal display elements has been conducted.
Liquid crystal panels are classified into transmission type crystal panels and reflection type crystal panels, according to their types. In the reflection type liquid crystal panels, a beam passes through a liquid crystal layer twice and consequently the thickness of the liquid crystal layer can be reduced by that amount as compared with the transmission type liquid crystal panels. As a result, the reflection type liquid crystal panels are excellent in fast response performance, and consequently they are suitable for dynamic picture display, i.e., application of projection type television.
On the other hand, in the transmission type liquid crystal panels, the so-called ON state and OFF state are generated by a shutter operation of the liquid crystal itself. In the case of the reflection type liquid crystal panels, both a beam in the ON state and a beam flux in the OFF state are reflected on the same optical path, and consequently a polarization beam splitter (hereafter abbreviated to PBS) for conducting beam separation on the basis of a difference in polarization state becomes an indispensable component.
The PBS action on a reflection type liquid crystal panel will now be described by using FIG. 12. In FIG. 12, reference numeral 1 denotes a PBS, 5 a cross prism for performing dichroic action, and 6 a reflection type liquid crystal panel. In FIG. 12, if light aligned with S-polarized light in an illumination optical system or only S-polarized light in the illumination optical system is input to the PBS 1, then the S-polarized light is reflected by a PBS plane of the PBS 1 and input to the cross prism 5. White light incident on the cross prism 5 is separated into three colors R, G and B by the dichroic action. The R, G and B colored beams are input to the reflection type liquid crystal panels 6 respectively corresponding to R, G and B. If each pixel is in the ON state in FIG. 12, then each of the beams input to the reflection type liquid crystal panels 6 respectively corresponding to R, G and B is converted in polarization state from S-polarized light to P-polarized light, and reflected. On the other hand, if each pixel is in the OFF state, then each beam is reflected while it is still S-polarized light. Beams of R, G and B input to the cross prism 5 again are subjected to color synthesis by the cross prism 5. As for beams incident on the PBS 1, each of beams in the ON state is a P-polarized beam and consequently it is transmitted through the PBS 1 this time, input to a projection lens (not illustrated), and projected. On the other hand, each of beams in the OFF state remains an S-polarized beam and consequently it is reflected by the PBS 1 again, and returned to its original light source side.
In a conventional reflection type liquid crystal display apparatus, it is necessary in the reflection type liquid crystal panel 6, which reflects both the ON beam and the OFF beam, to convert the polarization state of the ON beam from the S-polarized light to the P-polarized light, as described above. This holds true even if the S-polarized light and the P-polarized light are replaced with each other.
As for the polarization state of light that passes through the cross prism 5, therefore, for example, it is S-polarized light before it is reflected by the reflection type liquid crystal panel 6 and it is P-polarized light after it has been reflected by the reflection type liquid crystal panel 6. In the case where the cross prism 5 is used with S-polarized light and P-polarized light for the same wavelength, the wavelength characteristic in S-polarized light differs from that in P-polarized light. As a result, fine spectral transmission factor performance cannot be obtained. For example, desired image light of each color output from each reflection type liquid crystal panel 6 is not output from the cross prism 5.
Over against this problem, there has been proposed a scheme of separating one color from the white color by using a dichroic prism or a dichroic filter, converting a polarization state of one of two colors, and conducting color separation and synthesis by using the PBS. In this scheme, a total of three PBSs and one dichroic prism or dichroic filter are needed. Thus, this scheme is disadvantageous in size, weight and cost.
An object of the present invention is to make a polarization state of a beam incident on a reflection type liquid crystal panel the same as a polarized state of a reflected ON beam supplied from the reflection type liquid crystal panel in a configuration using a cross prism having a dichroic function and the reflection type liquid crystal panel, and thereby provide a small-sized, light-weighted, low cost illumination apparatus, and a projection type projector apparatus using the illumination apparatus.
In an optical unit including a light source, a polarization beam splitter, a color separation and synthesis unit having a dichroic function, and reflection type liquid crystal panels, a Faraday rotator is disposed on an optical path between the polarization beam splitter and the cross prism, and a polarization direction of a beam that passes through the Faraday rotator is rotated by a predetermined angle.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.